Thermionic tubes and the manufacture thereof



Se t. 21, 1937. F. s. M CULLOUGH THERMIONIC TUBES AND THE MANUFACTURE THEREOF Filed June 19, 1933 INVENTOR Patented Sept. 21, 1937 UNITED STATES PATENT OFFICE TBERDIIONIC TUBES AND THE MANUFAC- TUBE THEREOF Application June 19, 1933, Serial No. 676,418

Claims.

This invention relates to thermionic tubes and to an improvement in the manufacture of such tubes and is for an improvement on the invention disclosed in my co-pending application 5 Serial No. 571,578, filed October 28, 1931, now

Patent Number 1,991,767, February 19, 1935.

According to the present invention there is provided a thermionic tube construction in which the envelope of the tube is formed principally of metal. Moreover, there is provided a tube which isv complete after it comes oil the exhaust pump and does not have to be fitted with a base or cap. Moreover, the tubes may be constructed entirely without any glass, and the usual tubulation for exhausting the tube is not required.

Such tubes can be commercially constructed in very small sizes and yet perform the same work as the usual glass tube many times its size,

and they are particularly suited to the demand for an inexpensive tube which requires little space.

The present invention also provides a novel method in the manufacture of such tubes, and

more particularly in the method of sealing the tubes while the tubes are being exhausted, and without the usual glass tubulation. It further provides a novel arrangement for protecting certain portions of the tube from overheating while other portions are being heated to a high temperature for driving out the gases.

The invention may be readily understood by reference to the accompanying drawing which illustrates one embodiment of my invention and in which:

Figure 1 shows a vertical section through a tube and exhaust hose connection prior to the sealing of the tube; a

Figure 2 is a similar view after the tube has been sealed; and

Figure 3 is a front elevation of a complete tube embodying my invention, and the drawing shows on a full sized scale a commercially practical size tube embodying the present invention and capable of doing the same work as the common commercial radio tube now generally employed.

It will be seen by reference to Figs. 1 and 2 that these views are on a much larger scale than the full sized scale of Fig. 3.

Referring first to Fig. 1, the envelope of the tube is comprised principally of a piece of metal tubing 2 of a suitable diameter and of a suit- 55 able length. Nickel, or a nickel containing alloy,

is preferably used for this purpose. When a piece of tubing 2 has been provided, a ceramic base member 3 is fitted into the lower end of the tubing. Passing through this base member 3 are three contact pins 4, 5, and 6. The inner end of the contact pin 4 supports a grid electrode 5 I. The inner ends of the pins 5 and 6 are connected to a heater wire 8, which wire is supported in an insulator 9 inside a metal sheath or sleeve ill, the sheath or sleeve comprising the cathode of the tube. Preferably, these electrodes are as- 10 sembled on the insulator 3 before the insulator is inserted into the envelope 2. After the insulator has been inserted in the envelope, it is sealed in place. This sealing may be accomplished, if the material 3 is a low melting point 5 ceramic material, by heating the end of the tube and fusing the ceramic material directly to the metal, at the same time fusing the ceramic material around the pins 4, 5 and 6. If, however, the base 3 is of a high temperature ceramic material, it may be sealed in place by flowing a low melting point fusible material ii into the open end of the tube 3 over the bottom of the insulator 3 and around the pins 4, 5 and 6. In either event, a gas-tight seal is formed at the end of the tube.

Leading from the top of the cathode i0 is a wire I2. Inserted into the upper end of the tube 2 is an insulator l3 similar to the insulator 3, but having a central opening it. This insulator has a close fit in the tube and may be of a low fusing ceramic material sealed into the upper end of the tube by fusing it to the metal, or it may be sealed in place by the use of a low r fusing ceramic substance. The cathode lead wire i2 passes up through the opening l4 and is preferably made long enough to project a considerable distance beyond the end of the tube.

When the structure has been assembled this far, it is ready to be exhausted and sealed. For this purpose a gob of low fusing ceramic material I5 is placed about the wire i2, and the upper end of the tube is forced into the end of a thick rubber tubing 16 leading to an evacuating pump (not shown). Inside the tube Hi there is fitted a coil having an upper portion ll of relatively larger diameter and relatively larger wire, this part of the coil having a frictional engagement with the inside of the tube l6. Connected onto the lower end of the upper portion of the coil is a lower portion iii of relatively less diameter and of relatively smaller wire, the turns l8 being out of contact with the interior walls of the tube. The lower end of the turns l8 and the upper end of the turns H are connected together so that the coil forms a short-circuited loop. The low fusing ceramic material l5, when the tube is inserted in the rubber tubing, lies closely within the turns of the wire I8.

Below the end of the tubing l6 are two spaced apart cooling rings l9 and 20, the upper cooling ring :9 surrounding the upper portion of the tube 2 adjacent the disc l3 and the lower ring'20 sur rounding the lower portion of the tube just above the disc 3. Between the rings l9 and 20 is a coil 2| connected in circuit with a high frequency oscillator 22. Surrounding the end of the hose I6 is another coil 23 which is connected in circuit with a source of high frequency alternating current, such as an oscillator 24.

After the tube has been exhausted for a predetermined time. it is inductively heated by the passage of a high frequency current through the coil 2| to drive out additional gases. In this process of inductive heating the envelope 2, of course, becomes quite highly heated as well as do the electrodes within the tube. The cooling rings l9 and 20 cool those portions of the envelope adjacent the ceramic discs 3 and 13 to protect these discs from melting if they are formed. of a low fusing material, or to protect the low fusing material which seals them in place. This is course is accomplished by the circulation of a. cooling fluid through the cooling rings l9 and 20. After the tube has been based in this fashion it is ready to be sealed. To seal the tube a high frequency current is passed through the coil 23. This induces current in the coil l'l-l8, and the small wires l8 of this coil are heated to a point where they cause the low fusing ceramic material l to melt and flow down the wire into the opening 14. This material may spread out over the top of the disc l3, or it may merely plug the hole M. In

order to prevent the material from flowing entirely through the opening M, a small metal shield 25 is preferably secured to the wire 12 just below the opening l4 while the tube is being assembled. When the fused material 15 flows down into the opening I 4, it cools and thereupon seals the tube and the tube can be taken off the pump. When it is taken off it is a complete tube, the pins 4, 5 and 6 providing the base pins, so that no further base is provided. The wire l2 provides the cathode lead, and the metal shell tube comprises the plate of the tube and connection can be made directly to this tube.

The entire operation and assembly for pumping and sealing the tube can be carried out very rapidly, and the time required for pumping and i baking is very much reduced by reason of the smaller volume of the envelope than where there is a relatively large glass envelope. The sealing of the tube is simplified because there is no tubulation which has to be compressed, and the completed tube is one which is very rugged, there being no' thin glass in the construction either in the form of a tubulation or in the form of an envelope. It will be obvious 'to those skilled in the art that where additional electrodes are required these can be put into the assembly. It will also be understood that while the invention has particular application to the construction of small relatively inexpensive tubes, the invention is not limited to the manufacture of such tubes, but is also preferable to the manufacture of large tubes for various purposes.

It will be understood, however, that the drawing is merely illustrative of the invention and that various changes and modifications may be made in the construction and arrangement of the various parts within the contemplation of my invention and under the scope of the following claims.

I claim:

1. A thermionic tube comprising a cylindrical metal shell of substantially uniform diameter having a non-metallic base member sealed therein adjacentone end thereof and having contact pins passing therethrough and sealed therein, an indirectly heated cathode inside the tube having a heater wire connected to two of said contact pins, another electrode inside the tube connected to another of said contact pins, an insulating disc sealed into the opposite end of the tube and having a passageway therethrough, a cathode lead wire passing through said passageway and connected to said indirectly heated cathode, and a mass of sealing material fused about said cathode wire and into the passageway in the disc.

2. In the manufacture of vacuum tubes, the method which comprises assembling electrodes within a metal shell, providing an insulating disc having an opening therethrough at one end of said shell, connecting said end of the shell with a conduit leading to a vacuum pump to evacuate the tube, and then melting fusible sealing material in the conduit whereby such material flows over the opening in said insulator and effectively seals the tube.

3. In the manufacture of vacuum tubes, the steps which comprise assembling electrodes inside a metal shell which is sealed at one end. sealing a ceramic wall member into the opposite end, the wall member having an opening therein, connecting the shell with a vacuum pump in such manner that the tube may be evacuated through the opening in said wall member, and then fusing a gob of low melting material to said ceramic wall member over said opening and while the tube remains connected with the vacuum pump.

4. In the manufacture of vacuum tubes, the steps which comprise assembling electrodes inside a metal shell on a base of insulating material forming a closure for one end of the shell, sealing such base to the metal shell by the use of a fusible material, partially closing the other end of the shell by a disc having an opening therethrough and sealing such disc to the metal through the use of a fusible material, connecting said last mentioned end of the tube with a con.- duit leading to an evacuating pump, evacuating the tube, heating the tube to an elevated temperature to drive out heated gases and simultaneously cooling those portions of the tube which are adjacent the base and said disc, and thereafter flowing fused sealing material into the opening in said disc while the tube remains connected with the pump.

5. The method of making a thermionic tube having an envelope, comprising a metal shell which comprises mounting a number of electrodes on a common supporting member, providing a metal envelope having a bushing in its upper end, introducing the base member with the electrodes thereon to the bottom of the metal envelope in such manner that an upwardly extending wire projecting upwardly from the electrode assembly passes through said bushing sealing the base member to the envelope to make an air-tight joint, and sealing a gob of fusible material into the end of said bushing around said wire.

FREDERICK S. McCULLOUGH. 

